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1.
超声弹性成像有希望成为生物软组织病变诊断的有效手段,本文论述了软组织散射元准周期规则分布导致超声散射信号相干峰产生的机理,提出利用AR幅度倒谱估计散射元平均间距及其变化,结合组织外加应力来估计软组织内局部杨氏弹性模量,结果表明,该方法能有效地测量软组织内局部杨氏弹性模量,轴向和侧向空间分辨力分别为2.5mm和1.5mm,可用于在体软组织弹性成像,最后讨论了软组织弹性测量中的具体问题。  相似文献   

2.
超声弹性成像有希望成为生物软组织病变诊断的有效手段。本文论述了软组织散射元准周期规则分布导致超声散射信号相干峰产生的机理,提出利用AR幅度倒谱估计散射元平均间距及其变化,结合组织外加应力来估计软组织内局部杨氏弹性模量。结果表明,该方法能有效地测量软组织内局部杨氏弹性模量,轴向和侧向空间分辨力分别为2.5mm和1.5mm,可用于在体软组织弹性成像。最后讨论了软组织弹性测量中的具体问题。  相似文献   

3.
用电子散斑法对纯镍薄片弯曲变形的测量   总被引:4,自引:0,他引:4  
由于建立的电子散斑法有位移测量精度高、量程大的特点,且自制的力传感器灵敏度高、量程相对较大,从而保证了本实验中镍片在三点弯中的反应被全程、精确地记录下来.基于时间序列的电子散斑法,测出了10—100μm不同厚度的纯镍薄片在三点弯下的载荷-位移曲线,其中包括弹性部分以及进入塑性屈服两个阶段,据此可以推出不同厚度镍片的三点弯刚度.实验表明镍片的抗弯刚度受其厚度的影响很大,尤其在薄片厚度较小时表现得更为明显,即表现出明显的尺度效应.  相似文献   

4.
生物软组织力学活体测试技术进展   总被引:1,自引:0,他引:1  
成海平  刘正津 《力学进展》1995,25(3):401-409
本文综述了近年来有关生物软组织如皮肤、粘膜、肌腱、肌肉、神经和血管等活体状态下进行力学测试的新技术和新的试验装置,讨论了离体和活体生物力学性质之间存在差别的可能因素,以及活体生物软组织力学试验方法在临床应用中的意义。  相似文献   

5.
根据钢丝软轴基本参数的变化,确定其受载后其它几何尺寸的变化量,由此导出软轴两端相对扭转角进而得到钢丝软轴抗扭刚度的计算公式,此外,笔还在扭转试验机上对钢丝软轴的抗扭刚度进行实验测量,结果证实本理论计算值吻合于实际测量值。  相似文献   

6.
试验机弹性储能对岩石力学性能测试的影响   总被引:5,自引:0,他引:5  
在材料试验机上进行岩石力学性能测试时,如何准确测量岩石的变形是整个测试分析的基础.为了具体考察试验机刚度对岩石变形测量的影响程度,在两台不同的试验机上进行了岩石的单轴压缩试验,通过对加卸载过程中试验系统及岩石能量变化的分析,详细研究了试验系统弹性储能对岩石变形测量的影响,进而给出了基于试验机刚度的修正计算方法,来确定岩石在测试过程中的变形.  相似文献   

7.
生物软组织力学在研究生理、病理上具有很重要的地位。例如,动脉壁由于血压的作用而产生的应力和变形的问题,在了解心血管系统的生理和病理方面已得到了医学界的承认和重视。下面要谈生物软组织力学的另一方面的作用。  相似文献   

8.
目前中小桥梁日常安全巡检存在对检查人员依赖性高、缺乏可量化的科学依据等不足。针对这些问题,本文提出了一种利用高斯曲率极值点对结构进行损伤识别的方法。将桥面视为受弯弹性薄板,根据弹性薄板的弯曲理论得到了在荷载作用下结构刚度变化与桥面弯曲程度(高斯曲率)的理论关系,并由此推导了高斯曲率对结构刚度损伤的敏感程度公式。通过有限元建立了一座简支T梁模型,并在主梁肋板上设置不同高度、不同位置和不同数量的裂缝来模拟结构刚度损伤。计算了在自重作用下,裂缝高度、位置、数量与桥面高斯曲率变化的关系。分析结果表明,桥面的高斯曲率分布清晰地映射了结构的刚度分布,高斯曲率极值点明确地指征了桥梁的损伤位置。借力三维激光扫描等全息现代测量技术,本文的研究成果为高效量化的桥梁结构损伤识别提供了有效的分析手段。  相似文献   

9.
刚接或半刚性连接的组合梁在荷载作用下,在梁的长度范围内既有正弯矩作用段,又有负弯矩作用段,由于组合梁截面在正弯矩作用和负弯矩作用下截面抗弯刚度不一致,因而在弯矩为零的点处梁的截面抗弯刚度发生突变,而组合梁框架分析的关键是确定组合梁刚度突变分界点的位置及确定在整体分析中所采用的等效梁的刚度。本文根据应变能相等的原理对钢结构框架中组合梁的等效抗弯刚度进行了研究,推导了其等效刚度的表达式,并给出不同荷载作用形式下刚接框架组合梁等效刚度简化计算公式,为组合梁钢框架的整体分析提供了便利。最后分析了水平荷载以及梁柱连接特性对组合梁等效刚度的影响,分析结果表明,采用本文提出的组合梁等效刚度进行半刚性连接框架整体分析偏于安全。  相似文献   

10.
本文提出了用于岩土弹塑性有限元分析的隐式积分弹性刚度算法。该算法既具有隐式积分法精度好、效率高、无条件稳定等优点,也具有弹性刚度法中刚度矩阵正定、对称的特点,更重要的是它避免了传统切线刚度法在处理岩土非相关联塑性流动和屈服面“角点”所遇到的非对称性和奇异性计算问题。通过算例分析了该算法的精度、效率  相似文献   

11.
Luis A. Godoy 《Meccanica》2006,41(5):529-538
This paper studies the historical and epistemological approaches followed by historians of the theory of elasticity. The authors chosen are Todhunter and Pearson, Love, Timoshenko, and Truesdell, who are perhaps the most important historians in English language since the second half of the nineteenth century. It is shown that the historical purpose has changed from one historian to the next, ranging from history as a compilation of what is known to criticism of the evolution of elasticity. The path of progress is investigated and again there are significant differences between historians although overall they have a sense of confluence towards some form of truth. The relation between history and theory is identified as a recurrent theme. And the epistemology in each author, although not explicitly stated, is seen to change following the main trends in their times or before. Some possible avenues of research are mentioned towards the end.  相似文献   

12.
一种基于能量法则的爆炸成形弹丸速度的工程计算方法   总被引:1,自引:0,他引:1  
为了准确预报爆炸成形弹丸的速度,提出了以药型罩中所有内部微元都变处于流动状态的时刻作为爆炸成形弹丸成形结束的标志,并因此得出药型罩自身变形时所消耗的变形能应与使整个药型罩都处于流动状态的熔化能相等。在此基础上利用能量守恒原理,建立了爆炸成形弹丸速度的计算公式,并通过试验和数值模拟验证。实验和计算结果表明,本文中所建立的爆炸成形弹丸速度的计算公式具有较好的工程实用价值。  相似文献   

13.
A multimoment theory of elasticity of inhomogeneous media is used to develop algorithms for determining a sequence of essentially independent fundamental parameters associated with the structure, composition, and characteristics of the medium components. The general form of stress concentration factors is established by analyzing specific models of media. It is found that the mean tangential stresses in a fibrous medium with a transverse stress state are asymmetric. As an example, the methods are used to solve specific problems for plates and shells __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 1, pp. 66–76, January 2007.  相似文献   

14.
Semi-Lagrangian methods are now perhaps the most widely researched algorithms in connection with atmospheric flow simulation codes. In order to investigate their applicability to hydraulic problems, cubic Hermite polynomials are used as the interpolant technique. The main advantage of such an approach is the use of information from only two points. The derivatives are calculated and limited so as to produce a shape-preserving solution. The lack of conservation of semi-Lagrangian methods, however, is widely regarded as a serious disadvantage for hydraulic studies, where non-linear problems in which shocks may develop are often encountered. In this work we describe how to make the scheme conservative using an FCT approach. The method proposed does not guarantee an unconditional shock-capturing ability but is able to correctly reproduce the discontinuous flows common in open channel simulation without any shock-fitting algorithm. It is a cheap way to improve existing 1D semi-Lagrangian codes and allows stable calculations beyond the usual CFL limits. A basic semi-Lagrangian method is presented that provides excellent results for a linear problem: the new techniques allow us to tackle non-linear cases without unduly degrading the accuracy for the simpler problems. Two one-dimensional hydraulic problems are used as test cases, water hammer and dam break. In the latter case, because of the non-linearity, special care is needed with the low-order solution and we show the advantages of using Leveque's large-time step version of Roe's scheme for this purpose.  相似文献   

15.
For a beam subjected to electromagnetic force, magnetoelastic buckling due to the increase of such force is theoretically investigated by taking account of the nonlinearity of the electromagnetic force and the elastic force of the beam. Using Liapunov-Schmidt method and center manifold theory, the equilibrium space, the bifurcation set and the bifurcation diagram are theoretically derived. Also, the effect of the higher modes other than the buckling mode on the mode shape of the postbuckling state is discussed. Furthermore, a control method to stabilize the magnetoelastic buckling is proposed, and the unstable equilibrium state of the beam in the postbuckling state, i.e., the straight position of the beam, is stabilized by controlling the perturbation of the bifurcation.  相似文献   

16.
A technique is developed for determining the thermoviscoelastoplastic geometrically nonlinear axisymmetric stress–strain state of laminar shells of revolution under loads that induce meridional stress and torsion. The technique is based on the hypotheses of rectilinear element for the whole stack of layers. The relations of the theory of deformations along paths of small curvature are used as equations of state. The solution is reduced to the numerical integration of a system of ordinary differential equations. The technique is tried out by a test example and illustrated by determining the geometrically nonlinear thermoviscoelastoplastic state of a corrugated shell  相似文献   

17.
SHPB实验数据处理的规范化问题讨论   总被引:2,自引:0,他引:2  
从SHPB实验的一维应力假设出发,确定了入射、反射和透射波的起点位置的判读办法,提高了SHPB实验结果的准确性,并规范了SHPB实验的数据处理。另外,从动量守恒的角度,提出了标准入射波平台高度的判读办法。该方法可以避免弥散振荡对判读入射波平台高度的干扰,并排除人为因素的影响,提高了压杆应变片灵敏系数的标定准确性和标定过程的规范化程度。通过对比理论结果和数值模拟研究的结果,这两种数据处理方法的准确性得到了验证。  相似文献   

18.
In this paper, the wake effect on drag factor in the axisymmetric Oseen flow of the finite clusters of equally spaced spheres with same size is studied. Putting the Oseen lets on the centres of all the spheres, the series solution of the problem is obtained. By truncating the infinite series and applying the collocation method to solve a set of the linear algebraic equations, the approximate solution of the Oseen flow of finite clusters of spheres and the drag factor for each sphere are presented. The effect of the sphere number and spacing on the drag factor of each sphere under different Reynolds numbers are calculated and the wake effect as well as the shielding effect and the end effect are revealed. The influence of various parameters on the effects is considered and compared with the corresponding results of the Stokes flow. The convergence of the method is also studied numerically in this paper.  相似文献   

19.
This work investigates the trajectory method [1] for thereconstruction of ordinary differential equations (ODEs) from timeseries. The potentials of the method are analyzed for dynamical systemsdescribed by second- and third-order ODEs, focusing in particular on therole of the parameters of the method and on the influence of the qualityof the time series in terms of noise, length and sampling frequency.Typical models are investigated, such as the van der Pol, the linearmechanical, the Duffing and the Rössler equations, resulting in arobust and versatile method which is capable of allowing interestingapplications to experimental cases. The method is then applied to themeasured time series of a nonlinear mechanical oscillator, a typicalvelocity oscillation of the bursting phenomenon in near-wall turbulenceand the averaged annual evolution of rainfall, temperature andstreamflow over a hydrological basin.  相似文献   

20.
It is proved in this paper that the functionals of equivalent variational principles are different essentially only in terms of weighted residues. Consequently, the simplest method for constructing equivalent variational principles is to add weighted residues to known functionals as first used by Courant [4].  相似文献   

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